To make the jam base for the soufflé, blend the strawberries and 100g/4oz of the sugar in a blender or food processor to a pureé. Rub through a fine sieve into a heavy-bottomed pan. Scrape in the vanilla seeds from the pod. Bring to the boil over a medium heat, whisking continuously. Stir the cornflour with about four tablespoons of water just to slacken, then whisk into the strawberry pureé until the mixture thickens. Cool, then chill.
Brush the insides of four soufflé dishes that are 9cm/3½in diameter and 6cm/2½in deep with softened butter, then dust with caster sugar. Chill.
To make the sorbet, dissolve the 100g/4oz sugar in the boiling water, then simmer for two minutes to make a sugar syrup. Cool. In a blender or food processor, blend the strawberries with the syrup to a pureé, and rub through a fine sieve into a bowl. Cool, then chill. Place in an ice cream maker and churn for 15-20 minutes to a soft scoop texture. Scoop out four neat scoops and freeze on a plate. (The rest of the sorbet can be kept in the freezer for two weeks.)
To make the shortbread, beat the butter and icing sugar together, then gently mix in the flour and salt to make a dough. Roll into a cylinder about 5-6cm/2-2½in in diameter, wrap in cling film and chill in the fridge for at least two hours.
Preheat the oven to 200C/390F/Gas 6. Cut the chilled dough into 5mm/¼in thick slices (12-14 slices) and place on a baking sheet. Bake for 10-12 minutes or until golden around the edges. Slide onto a wire rack to cool and crisp. Leave the oven on.
To finish the soufflé, whisk the egg whites with the remaining 50g/2oz caster sugar to soft peaks. Fold into the soufflé jam base. Divide the mixture among the four dishes, filling them to the top, then level with the back of a knife. Bake for 9-11 minutes or until risen above the rim by half.
Remove from the oven and immediately dust the tops with icing sugar. Set each soufflé on a large plate. Put a frozen scoop of sorbet and a piece of shortbread to the side. Serve at once.